Directly compare raw XML files in CI

[parzhitsky]

Currently, to figure out whether the update is needed, there is a comparison between the currently published data.json file and a data.json file that would be built out of the latest XML file:

https://github.com/parzh/iso4217/blob/main/.github/workflows/publish-xml-updates.yml#L50-L58

Not only this introduces an unnecessary step of converting XML to JSON, but it also is prone to false positives in case if the potential new data.json file is in any way different (even if the change doesn't originate from the original data, – see #2):

{
  "$name": "SomeName",
  "$attr": {},
- "$data": 42
+ "$data": 42,
+ "$text": "42"
}

• Distrubite the original XML along with the converted JSON as data.xml;
• In CI, compare distributed data.xml with the XML content on maintainers' site;